The signal the HDMI output sends gets transfered pristinely and without degradation, however that signal is not a bit for bit identical copy of the file on the disc/hard drive, it is a converted version of that file, which to the best of my knowledge can not be reassembled on the receiving end to make an exact copy of the file from the original source. [Even if there weren't copy protection schemes in place to prevent it and pretending for the moment that there were stand alone recorders with HDMI in]. HDMI streaming is not the same as a USB file transfer.

I'm not arguing that the difference from device to device is audible, however. I'm just saying it's not a bit for bit accurate copy of the original file and may vary from device to device, which was the OP's question.

"Since all of the content will be transferred digitally to your display, this should result in perfect picture quality with no issues since "bits are bits", right? Unfortunately the reality is far more complex than this, and there are many factors that can come into play."

That quote is from this magazine and the article shows how there are many changes to the HDMI signal outputs between, for example, an OPPO and a Sony machine (that fails in some regards compared to the OPPO), using a very pricey Quantum Data HDMI Analyzer, however they unfortunately dont address the audio over the HDMI.

I guess everyone here (but me) thinks the audio is simply an unmodified S/PDIF signal and interchangeable between devices, however I'm not so sure. Machines modify their HDMI out video signals according to that magazine, so how can we be so sure they don't also manipulate their HDMI out audio signals?

The signal the HDMI output sends gets transfered pristinely and without degradation, however that signal is not a bit for bit identical copy of the file on the disc/hard drive, it is a converted version of that file, which to the best of my knowledge can not be reassembled on the receiving end to make an exact copy of the file from the original source. [Even if there weren't copy protection schemes in place to prevent it and pretending for the moment that there were stand alone recorders with HDMI in]. HDMI streaming is not the same as a USB file transfer.

You are correct. The file on the disc is compressed using a lossy codec. I'm not arguing that the data transmitted has any resemblance to the file on the disc. I'm saying the data transmitted, which is the decompressed output from the decoder in the player, will arrive perfectly intact at the destination.

If the decoder in the player has a bug or other issue in it's implementation then that decoded output may differ from another player, but either way HDMI will faithfully deliver the decoder output to the receiver.

Nope and that's why I didn't make that claim, but such amounts of jitter have a big measurable negative effect on SNR. I can imagine that it could be audible with highly dynamic recordings if you turn up the volume quite a bit.

If you are allowed to turn up the volume and listen to the noise floor, almost everything sounds different! Suddenly comparing a device with a noise floor 100 dB down becomes discernable from one that's 102 dB, with the right material and fast A/B switching, but in real world use it is completely meaningless and undetectable. [Not hard to believe since all of us would have no problem detecting a 2 dB change in audible hiss in real world conditions.]

"Poor" low level linearity down at those levels [when greatly amplified] also becomes audible, but similarly, in real world use, is completely meaningless and undetectable.

Unlike TCP, there is no retry if delivery of data failed, no guarantee of delivery. In fact, isochronous transfer is unidirectional.

The first part is correct.As an isochronous stream is a soft real time stream, a retry will always be too late.However USB in isochronous mode does reserve the appropriate bandwidth.So delivery is guaranteed downstream but delivering of the right bits is not

The second part is not correct.One can combine isochronous (thatís the way USB audio works) with 3 different type of synchronization.In case of synchronous or adaptive synchronization, the protocol is used unidirectional (the DAC adapts its clock speed to the incoming data stream).In case of asynchronous synchronization a feedback loop is established controlling the amount of data send by the PC. This allows the DAC to run with a fixed clock.In this case the protocol is used bi-directional.

As an isochronous stream is a soft real time stream, a retry will always be too late.

It probably would be too late, but typically there are no retries (see adaptive below).

QUOTE

However USB in isochronous mode does reserve the appropriate bandwidth.So delivery is guaranteed downstream but delivering of the right bits is not

If frames need to arrive every ms but do not it doesn't matter how much bandwidth is reserved. Also, most glitches occur because data doesn't arrive in time (DPC latency on Windows), not because of flipped bits.

The second part is not correct.

QUOTE

One can combine isochronous (that’s the way USB audio works) with 3 different type of synchronization.

If frames need to arrive every ms but do not it doesn't matter how much bandwidth is reserved. Also, most glitches occur because data doesn't arrive in time (DPC latency on Windows), not because of flipped bits.

It works slightly different.The frames always arrive in time, thatís the way USB works.The bandwidth is reserved on the hub to avoid interference of other USB devices.But this is downstream not upstream.The frames will always arrive in time but you might get glitches due to an insufficient amount of data in the frame e.g. due to DPC latency upstream

Nope and that's why I didn't make that claim, but such amounts of jitter have a big measurable negative effect on SNR. I can imagine that it could be audible with highly dynamic recordings if you turn up the volume quite a bit.

On the contrary, jitter noise is proportional to the amplitude of the signal, so in very quiet passages the jitter noise also becomes much smaller. Jitter has no effect whatever on silence.

So with that in mind if you wanted portable audiophile sound quality, all you'd need is any flac or wav player (quality not particularly important) with a digital out, good headphones and a good portable DAC? Does such a DAC exist? How do they compare to AV receivers?

I often use a Behringer UCA 202 ($30) with older laptops that have problematical audio interfaces. Its headphone amp leaves something to be desired with some headphones. The FIIO E7 seems to have a better headphone amp at a far higher cost, particularly in the area of providing a consistent low source impedance.

In general good portable equipment such as the Sansa Clip/Fuze perform about as well as a good AVR, other than power output. The headphone jack on a Clip/Fuze may outperform some AVR headphone jacks, particularly in the area of providing a consistent low source impedance.

If frames need to arrive every ms but do not it doesn't matter how much bandwidth is reserved. Also, most glitches occur because data doesn't arrive in time (DPC latency on Windows), not because of flipped bits.

It works slightly different.The frames always arrive in time, thatís the way USB works.The bandwidth is reserved on the hub to avoid interference of other USB devices.But this is downstream not upstream.The frames will always arrive in time but you might get glitches due to an insufficient amount of data in the frame e.g. due to DPC latency upstream

Nope and that's why I didn't make that claim, but such amounts of jitter have a big measurable negative effect on SNR. I can imagine that it could be audible with highly dynamic recordings if you turn up the volume quite a bit.

I don't know about SNR, but if it is really humongous, jitter can have an bad effect on THD+N. Not because it creates THD, but because the sidebands that jitter does create might be confused by the measuring technique with noise or harmonics.

As correctly stated by others, jitter has no effect on the noise floor again unless it becomes really huge and creates clicks and pops.

What's interesting is that as far as I can see, none of the technical data shown at the well-tempered computer page linked out of this thread actually shows jitter.

BTW I have heard a lot of jitter in my day, most intentionally created to mimic what I see in test reports, but at levels high enough to actually hear. Jitter seems to have a characteristic, generalizible sound. In general the subjective comments by high end reviewers don't seem to describe what I hear.

So you think a lot of people, including me (on my old notebook anyway), imagine audio glitches like VERY ANNOYING clicks or drop-outs with USB DACs? Screenshots of DPC latency measurements that clearly show that the hardware isn't able to stream audio glitch-free are anecdotes too?